Natural polymer-based slow-release oxygen microcapsule for repairing sediments as well as preparation method and application of natural polymer-based slow-release oxygen microcapsule

Abstract

The invention discloses a natural polymer-based slow-release oxygen microcapsule for repairing sediments as well as a preparation method and application of the natural polymer-based slow-release oxygen microcapsule. The slow-release oxygen microcapsule prepared by a micro-fluidic method comprises an oxygen release core containing calcium peroxide, sodium alginate and carboxymethyl chitosan are used as natural polymer shell materials, and the size of the slow-release oxygen microcapsule is 0.1-2 mm. The sodium alginate is subjected to ionic crosslinking between carboxyl and calcium ions to form an eggshell-shaped initial gel network; further, carboxymethyl chitosan is subjected to a Schiff base reaction through glutaraldehyde, and a second stable network is constructed; the two polymer chains form a composite shell layer with a stable structure and adjustable permeability through the synergistic effect of physical entanglement and double crosslinking points. The structure can effectively block water molecule permeation and oxygen diffusion, and long-acting release of oxygen is achieved.

Description

Technical Field

[0001] This invention pertains to environmental functional materials and water ecological restoration materials and methods, and particularly relates to a natural polymer-based slow-release oxygen microcapsule for sediment remediation, its preparation method, and its application. Background Technology

[0002] Hypoxia in water bodies and sediments is one of the core problems leading to black and odorous water bodies, endogenous pollution, and degradation of aquatic ecosystems. In stagnant or slow-flowing water bodies (such as lakes, reservoirs, rivers, and aquaculture ponds), organic matter accumulates in sediments and decomposes by consuming oxygen, easily creating anaerobic environments. Anaerobic environments not only promote the release of toxic and harmful substances such as ammonia nitrogen, hydrogen sulfide, and methane, exacerbating water pollution, but also inhibit the survival of benthic organisms and disrupt the ecological balance. Traditional water reoxygenation methods, such as surface aeration and mechanical agitation, mainly act on the overlying water body and have limited effect on improving the hypoxic state of sediments below the sediment-water interface, especially deep sediments. Furthermore, these methods suffer from drawbacks such as high energy consumption and the potential for secondary pollution caused by disturbing bottom sediments. Therefore, developing technologies that can directly act on the interior of sediments and achieve in-situ, long-term oxygen release is of practical significance for controlling endogenous pollution and restoring aquatic ecosystems.

[0003] To directly supply oxygen to sediments, solid peroxides (such as calcium peroxide) have become a research and application hotspot due to their ability to slowly release oxygen. However, unmodified peroxide particles face significant limitations in practical applications: their oxygen release process is greatly affected by environmental factors, often resulting in low oxygen utilization and short duration due to excessively rapid initial release, and may also stress benthic organisms due to drastic increases in local pH or excessive oxidation potential. To regulate the oxygen release process, slow-release coating technology has emerged. In existing technologies, coating with synthetic polymers or inorganic materials can achieve slow release to some extent, but some materials have poor biocompatibility, are difficult to degrade, and even pose risks of introducing secondary pollution, which contradicts the green and sustainable concept of ecological environment governance. Against this backdrop, constructing microcapsule shells with biodegradability and good environmental compatibility using natural polymer materials (such as sodium alginate and chitosan), with their unique three-dimensional network structure to achieve precise encapsulation and diffusion control of the oxygen-releasing core, is considered a promising new direction for achieving intelligent, long-term, and eco-friendly oxygen release. However, how to design and optimize the preparation process and structure of such natural polymer microcapsules to achieve stable, controllable and long-lasting oxygen release performance in complex sediment environments remains a key technical challenge that needs to be overcome. Summary of the Invention

[0004] Purpose of the invention: To overcome the shortcomings of existing technologies, this invention provides a natural polymer-based slow-release oxygen microcapsule for sediment remediation, its preparation method, and its application. It aims to overcome three major defects of traditional oxygen-releasing materials (such as CaO2) in sediment applications: first, the oxygen release rate is too fast and the action period is short; second, the oxygen release process is easily affected by water disturbance, and the generated oxygen bubbles easily escape into the atmosphere, resulting in low oxygen utilization; and third, the local microenvironment in the environment may cause acid shock.

[0005] This invention aims to achieve the slow and controllable release of oxygen by constructing a natural polymer microcapsule encapsulation system, and to effectively retain oxygen in the environmental medium by utilizing the pore structure and density characteristics of the microcapsules, thereby significantly extending its action time and utilization efficiency.

[0006] Sodium alginate undergoes ionic cross-linking between its carboxyl groups and calcium ions, forming an initial "eggshell"-like gel network. Subsequently, carboxymethyl chitosan undergoes a Schiff base reaction via glutaraldehyde, constructing a second, stable network. Through the synergistic effect of physical entanglement and the dual cross-linking points, the two polymer chains form a structurally robust and tunably permeable composite shell. This structure effectively blocks water molecule permeation and oxygen diffusion, enabling long-term oxygen release.

[0007] The technical solution of the present invention provides a natural polymer-based slow-release oxygen microcapsule for sediment remediation, comprising an oxygen-releasing core containing calcium peroxide and a composite shell covering the oxygen-releasing core; the composite shell is formed by sodium alginate and carboxymethyl chitosan through ionic crosslinking and covalent crosslinking. When the microcapsule is added to the sediment, the composite shell first undergoes hydration and swelling, and the internal calcium peroxide reacts with the infiltrated water molecules to generate oxygen and calcium ions, increasing the internal osmotic pressure and promoting the formation of regular nanoscale microporous channels in the shell.

[0008] Furthermore, the sediment is anoxic sediment; the oxygen release capacity of the microcapsules can reach 10-40 mg O2 / g, preferably 15-35 mg O2 / g based on the dry weight of the material.

[0009] Another aspect of the present invention provides a method for preparing the aforementioned natural polymer-based slow-release oxygen microcapsules for sediment remediation, comprising the following steps: (1) Preparation of porous material@calcium peroxide powder The porous material is made into powder, and the porous material powder is mixed with calcium chloride or calcium hydroxide powder and dissolved in deionized water. Then, ammonia water is added and an alkaline environment is maintained. Hydrogen peroxide solution is then added. After the reaction is completed, the solid product is separated, dried, and porous material@calcium peroxide powder is obtained. (2) Preparation of natural polymer mixed solution The obtained porous material@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed in a certain proportion to prepare a natural polymer mixed solution. (3) Preparation of oxygen-releasing microcapsules The mixed solution described in step (2) is added dropwise to a mixed solution containing a certain concentration of CaCl2 and glutaraldehyde. After the reaction, the product is obtained.

[0010] Further, in step (1), the porous material is one or more of biochar, activated carbon, zeolite, diatomaceous earth or attapulgite; the biochar is preferably wood charcoal, straw charcoal, microalgae charcoal, corn cob charcoal, mushroom charcoal or coconut shell charcoal.

[0011] Further, in step (1), the mass ratio of the porous material powder to calcium chloride or calcium hydroxide powder is 1:1-5.

[0012] Furthermore, in step (2), the mass ratio of porous material@calcium peroxide powder, sodium alginate and carboxymethyl chitosan is 1: 1-2: 2-4.

[0013] Furthermore, in step (3), the concentration of the CaCl2 solution is 10-500 mg / mL.

[0014] Further, in step (3), the content of glutaraldehyde in the mixed solution is 0.5-2.0 wt%. A third aspect of the present invention provides the application of the sustained-release oxygen microcapsules in anoxic deposits.

[0015] The slow-release oxygen mechanism of the microcapsules of this invention is as follows: When the microcapsules are added to anoxic sediments, their natural polymer shells (such as sodium alginate-chitosan) first undergo hydration and swelling. The internal calcium peroxide (CaO2) reacts with the infiltrated water molecules to produce oxygen and calcium ions. As the reaction proceeds, the internal osmotic pressure increases, prompting the shell to form regular nanoscale microporous channels. Oxygen molecules are continuously and slowly released into the pore water of the sediment through these diffusion channels. Simultaneously, the released calcium ions help maintain the pH stability and ion balance of the local microenvironment. The synergistic effect of the above processes achieves the slow release of oxygen, fundamentally improving the anaerobic state of the aquatic environment.

[0016] Compared with the prior art, the present invention has the following advantages: 1. Environmental friendliness: The natural polymer material used in the microcapsule shell has good biocompatibility and can be completely biodegraded in the natural environment, avoiding secondary pollution.

[0017] 2. Excellent physical properties: The microcapsules are uniform in size, with a controllable particle size within the range of 0.1-2 mm, which facilitates uniform dosing and precise metering in practical applications.

[0018] 3. Unique structural design, long-term and controllable oxygen release performance: The microcapsules have a dense surface shell and an internal three-dimensional network structure. This composite structure can effectively prevent water molecules from coming into contact with the internal calcium peroxide too quickly, and through the diffusion restriction effect of the network, it can synergistically regulate the slow and continuous release of oxygen, thereby changing the oxygen supply mode from a short burst to a long-term slow release.

[0019] 4. Clear oxygen release capacity: The oxygen release capacity of the microcapsules of this invention can reach 10-40 mg O2 / g (based on the dry weight of the material), which has a significant and quantifiable oxygen supply capacity and can effectively meet the long-term oxygen requirements of sediment remediation. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of the microcapsules of the present invention; Figure 2 This is a scanning electron microscope image of the microcapsules prepared according to the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0022] Example 1: (1) Preparation of charcoal@calcium peroxide powder The charcoal was cleaned, dried, and ground into powder. Then, the resulting charcoal powder and calcium chloride powder were dissolved in deionized water at a mass ratio of 1:2, and stirred for 12 hours. Subsequently, under ice-water bath conditions, an appropriate amount of ammonia was added to maintain the pH at 11. While continuously stirring, a specified volume of 30% hydrogen peroxide solution was added dropwise at a flow rate of 2 ml / min. After the reaction was complete, stirring was continued for 2 hours. Finally, the resulting mixture was filtered to separate the solid product, which was repeatedly washed with deionized water and dried at 70°C. (2) Preparation of natural polymer mixed solution The obtained charcoal@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed and dissolved in deionized water at a mass ratio of 1:2:4, wherein the concentration of charcoal@calcium peroxide powder was 10 g / L, the concentration of sodium alginate was 20 g / L, and the concentration of carboxymethyl chitosan was 40 g / L. The mixture was then dispersed using a homogenizer at 8000 rpm at room temperature until homogeneous, obtaining a uniform mixed solution. (3) Preparation of oxygen-releasing microcapsules Using microfluidic technology, the mixed solution described in step (2) was added dropwise to a mixed solution containing 50 mg / mL CaCl2 and 0.5 wt% glutaraldehyde at a flow rate of 100 μL / min. The reaction formed microcapsules, which were then aged in the mixed solution for 0.5 hours. Finally, the obtained microcapsules were repeatedly washed with distilled water and freeze-dried to obtain the natural polymer-based slow-release oxygen material; the oxygen release was 15 mg O2 / g.

[0023] Example 2: (1) Preparation of activated carbon@calcium peroxide powder Activated carbon was cleaned, dried, and ground into powder. The resulting activated carbon powder and calcium chloride powder were then dissolved in deionized water at a mass ratio of 1:4, and stirred for 16 hours. Subsequently, under ice-water bath conditions, an appropriate amount of ammonia was added to maintain the pH at 11. While continuously stirring, a specified volume of 30% hydrogen peroxide solution was added dropwise at a flow rate of 1.5 ml / min. After the reaction was complete, stirring was continued for 2 hours. Finally, the resulting mixture was filtered to separate the solid product, which was repeatedly washed with deionized water and dried at 70°C. (2) Preparation of natural polymer mixed solution The obtained activated carbon@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed and dissolved in deionized water at a mass ratio of 1:1:2, wherein the concentration of activated carbon@calcium peroxide powder was 10 g / L, the concentration of sodium alginate was 10 g / L, and the concentration of carboxymethyl chitosan was 20 g / L. The mixture was dispersed at 10,000 rpm using a homogenizer at room temperature until homogeneous, obtaining a uniform mixed solution. (3) Preparation of oxygen-releasing microcapsules Using microfluidic technology, the mixed solution described in step (2) was added dropwise to a mixed solution containing 20 mg / mL CaCl2 and 0.75 wt% glutaraldehyde at a flow rate of 150 μL / min. The reaction formed microcapsules, which were then aged in the mixed solution for 1 hour. Finally, the obtained microcapsules were repeatedly washed with distilled water and freeze-dried to obtain the natural polymer-based slow-release oxygen material; the oxygen release was 35 mg O2 / g.

[0024] Example 3: (1) Preparation of microalgae char@calcium peroxide powder The microalgae charcoal was cleaned, dried, and ground into powder. Then, the obtained microalgae charcoal powder and calcium chloride powder were dissolved in deionized water at a mass ratio of 1:3, and stirred for 12 hours. Subsequently, under ice-water bath conditions, an appropriate amount of ammonia water was added to maintain the pH at 12. While continuously stirring, a specified volume of 30% hydrogen peroxide solution was added dropwise at a flow rate of 2 ml / min. After the reaction was complete, stirring was continued for 2 hours. Finally, the resulting mixture was filtered to separate the solid product, which was repeatedly washed with deionized water and dried at 70°C. (2) Preparation of natural polymer mixed solution The obtained microalgae char@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed and dissolved in deionized water at a mass ratio of 1:2:2, wherein the concentration of microalgae char@calcium peroxide powder was 10 g / L, the concentration of sodium alginate was 20 g / L, and the concentration of carboxymethyl chitosan was 20 g / L. The mixture was dispersed at 12000 rpm using a homogenizer at room temperature until homogeneous, obtaining a uniform mixed solution. (3) Preparation of oxygen-releasing microcapsules Using microfluidic technology, the mixed solution described in step (2) was added dropwise to a mixed solution containing 100 mg / mL CaCl2 and 1.0 wt% glutaraldehyde at a flow rate of 50 μL / min. The reaction formed microcapsules, which were then aged in the mixed solution for 2 hours. Finally, the obtained microcapsules were repeatedly washed with distilled water and freeze-dried to obtain the natural polymer-based slow-release oxygen material; the oxygen release was 25 mg O2 / g.

[0025] Example 4: (1) Preparation of zeolite@calcium peroxide powder The zeolite was cleaned, dried, and ground into powder. Then, the resulting zeolite powder and calcium chloride powder were dissolved in deionized water at a mass ratio of 1:5, and stirred for 24 hours. Subsequently, under ice-water bath conditions, an appropriate amount of ammonia was added to maintain the pH at 10. While continuously stirring, a specified volume of 30% hydrogen peroxide solution was added dropwise at a flow rate of 1 ml / min. After the reaction was complete, stirring was continued for 2 hours. Finally, the resulting mixture was filtered to separate the solid product, which was repeatedly washed with deionized water and dried at 70°C. (2) Preparation of natural polymer mixed solution The obtained zeolite@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed and dissolved in deionized water at a mass ratio of 1:2:4, wherein the concentration of zeolite@calcium peroxide powder was 10 g / L, the concentration of sodium alginate was 20 g / L, and the concentration of carboxymethyl chitosan was 40 g / L. The mixture was then dispersed at 10,000 rpm using a homogenizer at room temperature until homogeneous, obtaining a uniform mixed solution. (3) Preparation of oxygen-releasing microcapsules Using microfluidic technology, the mixed solution described in step (2) was added dropwise to a mixed solution containing 150 mg / mL CaCl2 and 1.5 wt% glutaraldehyde at a flow rate of 200 μL / min. The reaction formed microcapsules, which were then aged in the mixed solution for 1.5 hours. Finally, the obtained microcapsules were repeatedly washed with distilled water and freeze-dried to obtain the natural polymer-based slow-release oxygen material; the oxygen release was 21 mg O2 / g.

[0026] Example 5: Preparation of corn cob char@calcium peroxide powder The corn cob charcoal was cleaned, dried, and ground into powder. Then, the obtained corn cob charcoal powder and calcium hydroxide powder were dissolved in deionized water at a mass ratio of 1:1 and stirred for 12 hours. Subsequently, under ice-water bath conditions, an appropriate amount of ammonia water was added to maintain the pH at 11. While continuously stirring, a specified volume of 30% hydrogen peroxide solution was added dropwise at a flow rate of 2 ml / min. After the reaction was complete, stirring was continued for 2 hours. Finally, the resulting mixture was filtered to separate the solid product, which was repeatedly washed with deionized water and dried at 70°C. (2) Preparation of natural polymer mixed solution The obtained corn cob char@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed and dissolved in deionized water at a mass ratio of 1:1:3, wherein the concentration of corn cob char@calcium peroxide powder was 10 g / L, the concentration of sodium alginate was 10 g / L, and the concentration of carboxymethyl chitosan was 30 g / L. The mixture was then dispersed using a homogenizer at 9000 rpm at room temperature until homogeneous, obtaining a uniform mixed solution. (3) Preparation of oxygen-releasing microcapsules Using microfluidic technology, the mixed solution described in step (2) was added dropwise to a mixed solution containing 200 mg / mL CaCl2 and 2.0 wt% glutaraldehyde at a flow rate of 300 μL / min. The reaction formed microcapsules, which were then aged in the mixed solution for 1 hour. Finally, the obtained microcapsules were repeatedly washed with distilled water and freeze-dried to obtain the natural polymer-based slow-release oxygen material; the oxygen release was 18 mg O2 / g.

[0027] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A natural polymer-based slow-release oxygen microcapsule for sediment remediation, characterized in that, It includes an oxygen-releasing core containing calcium peroxide and a composite shell covering the oxygen-releasing core; the composite shell is formed by sodium alginate and carboxymethyl chitosan through ionic crosslinking and covalent crosslinking. When the microcapsules are added to the sediment, the composite shell first undergoes hydration and swelling. The calcium peroxide inside reacts with the infiltrated water molecules to produce oxygen and calcium ions, and the internal osmotic pressure increases, which promotes the formation of regular nanoscale microporous channels in the shell.

2. The natural polymer-based slow-release oxygen microcapsules for sediment remediation according to claim 1, characterized in that, The sediment is anoxic sediment; the oxygen release capacity of the microcapsules can reach 10-40 mg O2 / g, preferably 15-35 mg O2 / g based on the dry weight of the material.

3. The method for preparing the natural polymer-based slow-release oxygen microcapsules for sediment remediation as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of porous material@calcium peroxide powder The porous material is made into powder, and the porous material powder is mixed with calcium chloride or calcium hydroxide powder and dissolved in deionized water. Then, ammonia water is added and an alkaline environment is maintained. Hydrogen peroxide solution is then added. After the reaction is completed, the solid product is separated, dried, and porous material@calcium peroxide powder is obtained. (2) Preparation of natural polymer mixed solution The obtained porous material@calcium peroxide powder, sodium alginate, and carboxymethyl chitosan were mixed in a certain proportion to prepare a natural polymer mixed solution. (3) Preparation of oxygen-releasing microcapsules The mixed solution described in step (2) is added dropwise to a mixed solution containing a certain concentration of CaCl2 and glutaraldehyde. After the reaction, the product is obtained.

4. The method according to claim 3, characterized in that, In step (1), the porous material is one or more of biochar, activated carbon, zeolite, diatomaceous earth or attapulgite; the biochar is preferably wood charcoal, straw charcoal, microalgae charcoal, corn cob charcoal, mushroom charcoal or coconut shell charcoal.

5. The method according to claim 3, characterized in that, In step (1), the mass ratio of the porous material powder to calcium chloride or calcium hydroxide powder is 1:1-5.

6. The method according to claim 3, characterized in that, In step (2), the mass ratio of porous material@calcium peroxide powder, sodium alginate and carboxymethyl chitosan is 1: 1-2: 2-4.

7. The method according to claim 3, characterized in that, In step (3), the concentration of the CaCl2 solution is 10-500 mg / mL.

8. The method according to claim 3, characterized in that, In step (3), the content of glutaraldehyde in the mixed solution is 0.5-2.0 wt%.

9. The use of the sustained-release oxygen microcapsules according to claim 1 or 2 in anoxic deposits.

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